1. Field of the Invention
The present invention relates to a disc centering device for centering an information carrier disc, such as a compact disc of the compact disc digital audio system as a digital audio disc, a video disc or the like which is to be placed on a turntable of a disc player such as a digital audio disc player and a video disc player.
2. Description of the Prior Art
In the disc player of the above-mentioned type, it is, as well known, necessary to center the information carrier disc on the turntable as accurate as possible in order to exactly catch signals recorded in the disc by means of a reproducing head.
For this purpose there has been proposed, for example, a disc clamping device for use in a compact disc player of the compact disc digital audo system, shown in FIG. 1, in which a turntable 1 is fixedly attached at its boss 2 around a rotation shaft 3 of a drive motor 4 which is fastened to a chassis 5. The turntable 1 is provided at the upper side thereof with a center spindle 6 of an annular wall shape projecting upwards coaxially with the boss 2 and having a diameter d slightly smaller than the outer diameter of the central aperture of a compact disc 9 and at the outer periphery of the upper side thereof with an annular disc supporting rib 7. The compact disc 9 is placed on the disc supporting rib 7 with the central aperture thereof fitted around the center spindle 6 having a guide taper surface 10 formed at its upper end. Then, the compact disc 9 so placed is depressed by a clamping plate 11, which is urged toward the turntable 1 by a downward force applied on the plate 11, and the disc 9 is thereby clamped between the clamping plate 11 and the disc supporting ridge 7 to achieve the attachment of the compact disc to the turntable 1.
In the above-described disc clamping device, a horizontal clearance between the center spindle 6 and the periphery of the central aperture of the disc 9 exists since the diameter of the central aperture is larger than the outer diameter of the center spindle 6 and hence the centering of the compact disc 9 is not accurately made. More specifically, the diameter D of the central aperture of the compact disc should be from 15-0 mm to 15+0.1 mm. On the other hand, the center spindle 6 is normally manufactured to have an outer diameter d of 14.90 to 14.95 mm in view of smooth fitting and removal of the compact disc with respect to the center spindle 6. Thus, the clearance D-d=0.2.about.0.05 mm occurs between the periphery of the central aperture of the disc 9 and the outer wall of the center spindle 6 and the compact disc 9 is hence set to the turntable 1 with a misalignment of 100.mu. to 25.mu.. In the compact disc player, even such a degree of misalignment can provide a disturbance to a tracking servo operation of the reproducing head.
FIG. 2 illustrates another typical example of the conventional centering device which is disclosed in U.S. Pat. No. 4,340,955. In this device, a drive motor 16 is mounted below a stationary platform 15 so that the rotation shaft 17 thereof vertically upwardly passes through an aperture formed through the platform 15. Around the rotation shaft 17 there is fixedly attached a concentric turntable 18 of a generally cylindrical cap shape having an annular flange 20, serving as a disc supporting portion, formed at its upper end. Above the turntable 18, a generally frustoconical centering member 22 is fitted around the rotation shaft 17 for vertical slide, the centering member 22 being provided at its periphery with a tapering surface 21. The centering member 22 is urged upwards by a spring 25.
To set a compact disc 26 to the turntable 18, the central aperture of the disc 26 is brought into engagement with the taper surface 21 of the centering member 22, and then a clamp member 27 is fitted around the rotation shaft 17 and is pressed downwards to thereby depress the disc 26 together with the centering member 22, thus clamping the disc 26 between the base portion of the clamp member 27 and the disc supporting portion 20 of the turntable 18. Thus, the prior art centering device shown in FIG. 2 is capable of accurately centering the disc about the axis of the rotation shaft 17 since the periphery of the central aperture of the compact disc 26 engages with the taper surface 21 of the centering member 22 in a fairly wide latitude in variation in the inner diameter of the central aperture.
However, this prior art device has a drawback in that the rather complicated structure thereof makes the assemblage thereof laborious thus raising the production cost. Further, the relative displacement of the centering member 22 relative to the turntable 18 inevitably produces a play between them, which makes it unable to carry out the centering of the disc in a high degree. In addition, when the centering member 22 does not smoothly slide along the rotation shaft 17 due to a tight engagement, the smooth centering of the disc 26 cannot be achieved.